This invention relates to the art involving cleaning devices which are used to remove deposits of soot, dirt and debris from heat exchange tube surfaces and particularly on the surfaces of tubes used in connection with furnaces and boilers. To remove such deposits, it has long been customary to use air or steam under high pressure to literally blow the deposits off the tubes and thus prevent the deposits from becoming a layer of insulation which would reduce the exchange or transfer of heat by the tubes and adversely affect their function. Such means are usually referred to in the trade as soot blowers.
The heat exchange tubes are customarily provided in banks or clusters. The hot combustion gases from the boiler or furnace pass over these banks of tubes which absorb the heat therefrom and thus heat the contents of each tube in the usual heat exchange function. In so doing, the exterior of the tubes collect dust or soot emitting from the furnace or boiler which makes the tubes less effective as heat exchange units unless thoroughly cleansed from time to time.
The problems involved in the deposit of dust or soot on or in heat exchange tubes have long been realized, and many attempts have been made to overcome these problems. Among these attempts are the structures set forth in the following U.S. Pat. Nos.: 1,677,383; 1,688,482; 1,760,589; 1,811,346; 1,896,565; 2,001,881; 2,112,896; 2,406,687; 2,696,016; 2,710,225; 3,049,738; 3,068,507; 3,138,819; 3,115,016; 3,184,774; 3,191,211; 3,436,786; 3,448,477; 3,794,051.
While, as aforesaid, many attempts have been suggested to overcome the problems, two structures are for the most part in commercial use.
One of the commercially used soot blowers utilizes a tube, called a lance, which extends across the width of the tube bank. The lance is provided with apertures or nozzles extending thereover at pre-determined spaced distances. High pressure steam is introduced into the lance and this steam emits through the various nozzles in order to enable jets of steam to pass therethrough and blow away the soot, dust and other debris. This device is usually provided with motor driven means disposed exteriorly of the furnace whereby the lance is continuously rotated through 360.degree. continuing cycles thus attempting to blow the soot and debris away in a complete circle around the lance. This type cannot accommodate a flexible hose feed for the steam supply as it would become overly twisted and block the passage. Thus it was necessary to use seals between a rigid steam supply pipe and the rotating lance, and it also has been found that the soot blowing range of any one lance is very limited because the steam velocity decreases rapidly as it leaves each nozzle. Thus soot blowers of this type must be mounted in proximity to each other along the length of the bank of tubes which is a relatively costly arrangement.
In addition, such soot blowers have other disadvantages. Among them is the arrangement whereby the lances remain interiorly of the housing carrying the banks of tubes when not in use. Thus the lances are exposed to the condition or atmosphere of the hot corrosive flue gases at all times which causes the lance to deteriorate and necessitates eventual replacement of the lances or use of an expensive corrosion resistant alloy. Furthermore, the lances, as aforesaid, are multi-nozzled or apertured. In fact, customarily, nozzles are provided every 8 to 12 inches along the length of the lance in order to assure its effectiveness. As this system is used in furnaces of varying widths including extremely wide furnaces, many nozzles are required. It has been found that in order to be effective, each jet nozzle requires a flow rate of thousands of pounds an hour to provide the high momentum needed to effectively clean the banks of tubes. Obviously, with the number of steam nozzles required per lance, it is necessary to install an expensive steam generator because of the high simultaneous capacity required. Since sootblowing is carried out for a small fraction of the time that the boiler or furnace operates, the expensive steam generating capacity is idle most of the time.
Another soot blower in current commercial use is one which also constantly rotates through 360.degree. continuous cycles but is insertable and retractable. Such a soot blower is described in U.S. Pat. No. 2,696,016. In this device, a "lance" is also utilized but of a slightly different construction. This lance has two opposed nozzles at its terminus and rotates as it is advanced into the tube. The lance continuously rotates a full 360.degree. in continuing cycles throughout the entire width of the tube bank. Furthermore, a reversing mechanism is provided to retract the lance after it reaches the end of its forward travel and it is brought back to a position outside of the housing containing the tube bank. Because there are only two jet nozzles, the steam generation capacity required is much smaller and there is a consequent saving in capital investment. In addition, the stored position of the lance outside of the furnace prevents it from becoming subject to the destructive effects of the hot corrosive flue gases.
However, the aforesaid construction has specific disadvantages. For example, a separate lance is required at predetermined spaced intervals along the length of the tube bank because the effective area which may be cleaned by the soot blower is quite limited extending only to about a 3 or 4 foot radius. In addition, there is a solid steam supply tube which is stationary and the lance rotates therearound. As a result, costly seals must also be provided in the construction between the rotating lance and its interior supply tube. As a result of the high pressure required in the steam supply, it has been found that no matter how effective the original seal, deterioration and steam leaks regularly develop and constant maintenance and expensive replacement is required.
The soot blower of the present invention overcomes the problems described above with regard to these commercial soot blowers presently provided and presents a unit which is extremely efficient while requiring only a minimum amount of parts and little maintenance while nonetheless effectively cleaning the surfaces of the tube banks in an extremely efficient manner.